Natural selection of Varroa jacobsoni explains the different reproductive strategies in colonies of Apis cerana and Apis mellifera

In colonies of European Apis mellifera, Varroa jacobsoni reproduces both in drone and in worker cells. In colonies of its original Asian host, Apis ce rana, the mites invade both drone and worker brood cells, but reproduce onl y in drone cells. Absence of reproduction in worker cells is probably cruci al for the tolerance of A. cerana towards V. jacobsoni because it implies t hat the mite population can only grow during periods in which drones are re ared To test if non-reproduction of V. jacobsoni in worker brood cells of A . cerana is due to a trait of the mites or of the honey-bee species, mites from bees in A. mellifera colonies were artificially introduced into A. cer ana worker brood cells and vice versa. Approximately 80% of the mites from A. mellifera colonies reproduced in naturally infested worker cells as well as when introduced into worker cells of A. mellifera and A. cerana. Conver sely, only 10% of the mites from A. cerana colonies reproduced, both in nat urally infested worker cells of A. cerana and when introduced into worker c ells of A. mellifera. Hence, absence of reproduction in worker cells is due to a trait of the mites. Additional experiments showed that A. cerana bees removed 84% of the worker brood that was artificially infested with mites from A. mellifera colonies. Brood removal started 2 days after artificial i nfestation, which suggests that the bees responded to behaviour of the mite s. Since removal behaviour of the bees will have a large impact on fitness of the mites, it probably plays an important role in selection for differen tial reproductive strategies. Our findings have large implications for sele ction programmes to breed less-susceptible bee strains. If differences in n on-reproduction are mite specific, we should not only look for non-reproduc tion as such, but for colonies in which non reproduction in worker cells is selected. Hence, in selection programmes fitness of mites that reproduce i n both drone and worker cells should be compared to fitness of mites that r eproduce only in drone cells. Exp Appl Acarol 23: 133-144 (C) 1999 Kluwer A cademic Publishers.